1. Field of the Invention
The present invention relates to a light-emitting device containing a phosphorescent metal complex having an organic ligand, and a display apparatus including the light-emitting device.
2. Related Background Art
There has been known an organic electroluminescence device (hereinafter, also referred to as “organic EL device”) as a light-emitting device.
The organic EL device has at least one organic layer provided between electrodes. An organic layer may have a multi-layer structure, for example, a three-layer structure including a hole transporting layer, a light-emitting layer, and an electron transporting layer, or a four-layer structure including a hole transporting layer, a light-emitting layer, an exciton diffusion blocking layer, and an electron transporting layer.
The hole transporting layer may be composed of α-NPD. The light-emitting layer may be composed of Alq3, CBP as a host doped with Ir(ppy)3 or CBP as a host doped with PtOEP. The exciton diffusion blocking layer may be composed of BCP. The respective compounds are listed below in full.    Alq3: aluminum-quinolinol complex    α-NPD: N4,N4′-Di-naphthalen-1-yl-N4,N4′-diphenyl-biphenyl-4,4′-diamine    CBP: 4,4′-N,N′-dicarbazole-biphenyl    BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline    PtOEP: platinum octaethylporphyrin complex    Ir(ppy)3: iridium-phenylpyridine complexThe structures of the above compounds except PtOEP are shown in FIG. 3.
Also, an electron transporting material includes oxadiazole derivatives.
Examples of an organic EL device making use of phosphorescence are reported in, for example, “Improved Energy Transfer in Electrophosphorescent Device” (D. F. O'Brien et al., Applied Physics Letters Vol. 74, No. 3, p. 422 (1999)) and “Very High-efficiency Green Organic Light-emitting Devices based on Electrophosphorescence” (M. A. Baldo et al., Applied Physics Letters Vol. 75, No. 1, p. 4 (1999)).
The technique of converting an excitation energy from triplet excitation to singlet excitation is disclosed by U.S. Pat. No. 6,310,361, Applied Physics Letters: 79, 7, 1045 (2001), and Nature: Vol. 403, 750 (2000).
Besides, Japanese Patent Application Laid-Open No. 2003-077674 discloses that an energy is converted from a triplet exciton to triplet excitation and light is emitted from the triplet excitation.
However, none of the above techniques offer a satisfactory device in terms of phosphorescence efficiency, device lifetime, and power consumption.